The disclosure of Japanese Patent Application No. 11-183062 filed on Jun. 29, 1999 including the specification, drawings and abstract is incorporated herein by reference in its entirety.
1. Field of Invention
The present invention relates to a technology for automatically stopping and starting an internal combustion engine installed in a motor vehicle.
2. Description of Related Art
In order to reduce the fuel consumption of and the emissions and noise from internal combustion engines installed in motor vehicles and the like, automatic stop-start apparatus for automatically stopping the operation of a vehicle-installed internal combustion engine during a stoppage of the vehicle (e.g., during a red traffic light or the like) and automatically starting the engine when the vehicle begins to move have been pursued.
There is a widely known automotive brake mechanism that has a brake booster for boosting the brake operating force from a driving person by using a negative pressure that occurs in an intake passage of an internal combustion engine (intake pipe negative pressure).
In this brake mechanism, an intake pipe negative pressure occurring in the intake passage is constantly supplied to the brake booster when the internal combustion engine is in operation. Therefore, if a negative pressure in the brake booster is consumed for a braking operation, the amount of pressure consumed is offset by an intake pipe negative pressure from the intake passage.
When the internal combustion engine is in an automatically stopped state, no intake pipe negative pressure occurs in the intake passage, so that no negative pressure is supplied from the intake passage to the brake booster. Therefore, if an automatic engine stop-start technology is applied to a motor vehicle equipped with the above-described brake mechanism, the following problem may occur. For example, when the motor vehicle is stopped on a slope and a negative pressure in the brake booster is consumed by a braking operation, the amount of pressure consumed is not compensated for. In that case, the amount of assist force that can be produced by the brake booster decreases, and the amount of brake-operating force that needs to be provided by a driving person correspondingly increases.
Japanese Patent Application Laid-Open No. 58-35245 discloses an automatic engine stop-start apparatus for coping with the aforementioned problem. If the pressure in the brake booster exceeds a predetermined value (that is, if the degree of negative pressure in the brake booster becomes less than a predetermined value) due to a driving person""s braking operation while the engine is in the automatically stopped state, the apparatus warns the driving person, or automatically starts the engine while warning the driving person, to produce an intake pipe negative pressure and supply the intake pipe negative pressure to the brake booster. In this manner, the apparatus secures a brake booster negative pressure needed to boost the brake operating force.
Since the negative pressure in the brake booster is a relative pressure between the pressure in the brake booster and the atmospheric pressure, the brake booster negative pressure changes in magnitude with changes in the atmospheric pressure even if the pressure in the brake booster remains unchanged.
The above-described automatic engine stop-start apparatus uses a fixed criterion (predetermined value) to evaluate the brake booster negative pressure, and does not take changes in the atmospheric pressure into consideration. Therefore, in the apparatus, it is difficult to accurately evaluate the degree of brake booster negative pressure when the engine is in the automatically stopped state.
More specifically, at locations where the atmospheric pressure is relatively low, for example, at high altitudes or the like, it is difficult to accurately evaluate the degree of brake booster negative pressure.
Accordingly, it is an object of the invention to provide a technology for automatically stopping and automatically starting an internal combustion engine in a vehicle equipped with a brake booster that uses the negative pressure in an intake pipe of the engine, while securing a sufficient brake booster negative pressure in accordance with changes in the atmospheric pressure.
To achieve the aforementioned and/or other objects, a control apparatus for an internal combustion engine in accordance with one aspect of the invention includes a pressure detector that detects a pressure in the brake booster, and a controller that automatically stops the internal combustion engine when a predetermined stop condition is met, and that automatically starts the internal combustion engine when a predetermined start condition is met. The controller also outputs a warning and/or performs an engine restart operation when the pressure detected by the pressure detector exceeds a reference value while the internal combustion engine is automatically stopped. The controller also can change the reference value in accordance with an atmospheric pressure.
Therefore, if the actual degree of negative pressure in the brake booster decreases during the automatically stopped state of the engine, the apparatus is able to immediately start the engine or advise a driving person to start the engine. As a result, the intake pipe negative pressure that occurs in the intake pipe of the engine is supplied to the brake booster, so that a sufficient negative pressure is reliably provided in the brake booster.